Electric drive machines are quickly replacing mechanical drive machines both in on-highway and off-highway applications. An electric drive machine consists generally of an engine drivingly coupled to a generator. As a mixture of fuel and air is burned within the engine, a mechanical rotation is created that drives the generator to produce electric power. The electric power is sent to one or more motors associated with traction devices of the machine to propel and steer the machine.
Conventionally, the speed of an electric drive machine is controlled by commanding the motors to produce a particular torque. However, in a multi-path drive system, where each motor is independently controlled, a difference in output speeds of the motors can be observed as the motors encounter varying torque loads. This difference in output speeds can result in unintended steering of the associated machine.
One attempt to control steering in a dual-path electric drive machine is disclosed in U.S. Pat. No. 7,578,361 (the '361 patent) that issued to Thacher on Aug. 25, 2009. In particular, the '361 patent discloses a differential steering assist system for an off-road utility vehicle. The off-road utility vehicle includes left and right front wheels that are steerable, and left and right rear wheels that are independently driven by associated electric motors based on differences between commanded and desired output torque. The differential steering assist system uses a steering position sensor to sense a steering position of the front wheels, and wheel speed sensors to sense the speeds of the rear wheels. An electronic control unit selectively provides speed-reducing commands to the left or right rear wheels based on the steering position and the wheel speeds to thereby assist the vehicle in steering.
Although the differential steering assist system of the '361 patent may help an off-road utility vehicle during intentional steering, it may have limited applicability and benefit. In particular, the system may only be applicable to a vehicle that has steerable front wheels. In addition, the system may not help maintain straight travel of the vehicle when steering is undesired.
The disclosed steering control system is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.